Why Are Returning Favorites Returning to Fewer Viewers?

Ellen Pompeo in Grey's Anatomy by Mitch Haddad/ABC
A not-so-funny thing happened last Thursday: ABC's
Ugly Betty and
Grey's Anatomy fared "well" against their venerable CBS competition, yet delivered their lowest ratings
ever, falling 27 percent and 22 percent (respectively) below their prior season averages.
Similarly, Fox's
House is down markedly from its season average, though a good deal of that trend can be ascribed to its Monday time slot and thus the absence of an
Idol lead-in.
Shouldn't the hottest shows on television be getting welcomed back by throngs of impassioned, for-too-long-deprived-by-the-strike viewers?
Or could it be that the WGA strike - as did O.J. Simpson and Judge Ito back in the day - afford people the opportunity to realize that (some semblance of a) life can go on
sans television?
What's your take? How can it be that ratings are not as robust as they were before the strike? Were we not all sitting by the remote anxiously waiting for the TV season to resume?